The user needs to activate a function or issue a command.

Interactive Example

Click the button to see its two states.

Context

This command button allows single activation of a safety-relevant command or function.

Forces

The button may be too small so the error rate could increase. Hitting the touch screen may cause inadvertent double activation of the command, similar to a double click. Some touch screens are not very accurate in interpreting touch input, which may also cause multiple activation of a command.

Solution

This simple command button has a minimum size as described in the respective pattern and has a text label using a font with a defined minimum size and, optionally, an icon with at least 16 x 16 pixels in size. The command button has a safety area around it with a minimum spacing to the next control.

The button responds only to one single click and immediately releases after being pressed. It has a debounce timer attached to prevent inadvertent activation.

Usability Impact

Error prevention, user satisfaction

Safety Impact

The minimum size and the safety padding guarantee that the button can easily be pressed without inadvertently activating a neighbouring control.

The built in button debounce secures the button against unintentional multiple activation.

Usage

Has been used in several European railways voice communication devices. It was used when answering calls with a button to avoid the calls being ended unintentionally.